Debt instrument, interest payment maximum deferral of consecutive quarterly periods.

No definition available.

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Namespace Prefix:	sr_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument interest rate reviving period.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument maturity year.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument minimum resetting interest rate.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt instrument, redemption price, percentage of principal and interest payments.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of total capitalization in the covenant of line of credit facility.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Maximum consolidated capitalization ratio percentage.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of change of control of principal and accrued interest.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of short-term borrowing used to support lending to utilities.

+ References

No definition available.

+ Details

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Namespace Prefix:	sr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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Period Type:	instant

- Definition

Date when the debt instrument is scheduled to be fully repaid, in YYYY-MM-DD format.

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Balance Type:	na
Period Type:	duration

- Definition

Description of the payment terms of the debt instrument (for example, whether periodic payments include principal and frequency of payments) and discussion about any contingencies associated with the payment.

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- Definition

Description of debt redemption features under terms of the debt agreement.

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

+ Details

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- Definition

Period between issuance and maturity of debt instrument, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Balance Type:	na
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- Definition

The cash outflow for the extinguishment of long-term borrowing, with the highest claim on the assets of the entity in case of bankruptcy or liquidation, before its maturity.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date the credit facility terminates, in YYYY-MM-DD format.

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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Description of when the fee for available but unused credit capacity is required to be paid (for example, annually, quarterly, or monthly).

+ References

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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Data Type:	dtr-types:percentItemType
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- Definition

The percentage rate used to calculate dividend payments on preferred stock.

+ References

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Period Type:	duration

- Definition

Value of the difference between preference in liquidation and the par or stated values of the preferred shares.

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- Definition

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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Financing - Additional Information (Details)									1 Months Ended	9 Months Ended
Financing - Additional Information (Details)	Mar. 26, 2026 USD ($)	Feb. 19, 2026 USD ($)	Feb. 09, 2026 USD ($)	Jan. 29, 2026	Jan. 12, 2026 USD ($) qtr	Dec. 17, 2025 USD ($)	Nov. 24, 2025 USD ($)	Oct. 23, 2025 USD ($)	Feb. 28, 2026 USD ($) shares	Jun. 30, 2026 USD ($)	Mar. 31, 2026 USD ($)	Dec. 31, 2025 USD ($)	Sep. 30, 2025 USD ($)	Jun. 30, 2025 USD ($)
Short-Term Debt [Line Items]
Borrowings outstanding										$ 1,263,500,000			$ 1,317,000,000	$ 1,009,500,000
Depositary Shares [Member]
Short-Term Debt [Line Items]
Preferred Stock, Shares Outstanding, Ending Balance \| shares									10,000,000
Series A Preferred Stock [Member]
Short-Term Debt [Line Items]
Preferred stock percentage				5.90%					5.90%
Aggregate liquidation preference									$ 250,000,000
Parent Company [Member] \| First Mortgage Bond [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount								$ 200,000,000
Debt instrument, payment terms								semi-annually on March 15 and September 15 of each year
Parent Company [Member] \| First Mortgage Bond [Member] \| Share-Based Payment Arrangement, Tranche One [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount								$ 150,000,000
Debt instrument interest rate stated percentage								4.60%
Debt instrument maturity date								Sep. 15, 2030
Parent Company [Member] \| First Mortgage Bond [Member] \| Share-Based Payment Arrangement, Tranche Two [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount								$ 50,000,000
Debt instrument interest rate stated percentage								4.65%
Debt instrument maturity date								Jan. 15, 2031
Commercial Paper [Member] \| Parent Company [Member]
Short-Term Debt [Line Items]
Borrowings outstanding										1,263,500,000			$ 1,317,000,000	$ 1,009,500,000
Short term borrowings used to support lending to utilities										652,100,000
Maximum [Member] \| Commercial Paper [Member]
Short-Term Debt [Line Items]
Borrowings outstanding										1,500,000,000
Spire [Member] \| Junior Subordinated Notes [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount							$ 900,000,000
Debt instrument, payment terms							Interest is payable semiannually on June 1 and December 1, beginning June 1, 2026.
Debt instrument redemption price percentage							100.00%
Debt instrument redemption description							(i) at any time during the 90‑day period prior to the first reset date and (ii) on any interest payment date after the first reset date; they may also be redeemed at par within 120 days following a Tax Event or at 102% within 120 days following a Rating Agency Event, in each case plus accrued interest to (but excluding) the redemption date.
Spire [Member] \| 2025 Series A Junior Subordinated Notes [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount							$ 450,000,000
Debt instrument maturity year							2056
Debt instrument interest rate reviving period							5 years
Debt instrument basis spread on variable rate							2.556%
Debt instrument minimum resetting interest rate							6.25%
Debt instrument interest rate stated percentage							6.25%
Debt instrument maturity date							Jun. 01, 2031
Spire [Member] \| 2025 Series B Junior Subordinated Notes [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount							$ 450,000,000
Debt instrument maturity year							2056
Debt instrument interest rate reviving period							5 years
Debt instrument basis spread on variable rate							2.327%
Debt instrument minimum resetting interest rate							6.45%
Debt instrument interest rate stated percentage							6.45%
Debt instrument maturity date							Jun. 01, 2036
Spire [Member] \| Series 2026 Senior Notes [Member] \| Master Note Purchase Agreement [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount						$ 825,000,000
Maximum consolidated capitalization ratio percentage						70.00%
Percentage of change of control of principal and accrued interest						100.00%
Spire [Member] \| 4.6% Senior Notes due 2031 [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount			$ 400,000,000
Debt instrument interest rate stated percentage			4.60%
Debt instrument maturity date			Sep. 01, 2031
Debt instrument, payment terms			Interest on the 2031 Senior Notes is payable semiannually on March 1 and September 1, beginning September 1, 2026.
Debt instrument, redemption price, percentage of principal and interest payments			0.15%
Debt instrument redemption description			Prior to August 1, 2031, the Company may redeem the 2031 Senior Notes, in whole or in part, at a redemption price equal to the greater of (i) the present value of the remaining scheduled principal and interest payments (discounted at the applicable Treasury Rate plus 15 basis points) minus accrued interest, or (ii) 100% of principal, plus accrued and unpaid interest to, but excluding, the redemption date. On or after August 1, 2031, the notes may be redeemed at 100% of principal plus accrued interest.
Spire [Member] \| 4.6% Senior Notes due 2031 [Member] \| Prior to August 1, 2031 [Member]
Short-Term Debt [Line Items]
Debt instrument redemption price percentage			100.00%
Spire [Member] \| 4.6% Senior Notes due 2031 [Member] \| On or after August 1, 2031 [Member]
Short-Term Debt [Line Items]
Debt instrument redemption price percentage			100.00%
Spire [Member] \| 5.300% Senior Notes due March 1, 2026 [Member]
Short-Term Debt [Line Items]
Debt instrument interest rate stated percentage			5.30%
Early repayment of debt		$ 350,000,000
Spire [Member] \| 6.375% Junior Subordinated Notes due 2086 [Member]
Short-Term Debt [Line Items]
Debt Instrument face amount					$ 200,000,000
Debt instrument interest rate stated percentage					6.375%
Debt instrument maturity date					Mar. 01, 2086
Debt instrument, payment terms					The Notes bear interest at 6.375%, payable quarterly beginning June 1, 2026
Interest payment, maximum deferral of consecutive quarterly periods \| qtr					40
Spire [Member] \| 6.375% Junior Subordinated Notes due 2086 [Member] \| On or After March 1, 2031 [Member]
Short-Term Debt [Line Items]
Debt instrument redemption price percentage					100.00%
Spire [Member] \| 6.375% Junior Subordinated Notes due 2086 [Member] \| Prior to March 1, 2031 upon Occurrence of Tax Event [Member]
Short-Term Debt [Line Items]
Debt instrument redemption price percentage					100.00%
Spire [Member] \| 6.375% Junior Subordinated Notes due 2086 [Member] \| Prior to March 1, 2031 upon Occurrence of Rating Agency Event [Member]
Short-Term Debt [Line Items]
Debt instrument redemption price percentage					102.00%
Spire [Member] \| Minimum [Member] \| Series 2026 Senior Notes [Member] \| Master Note Purchase Agreement [Member]
Short-Term Debt [Line Items]
Debt instrument interest rate stated percentage						4.59%
Debt instrument maturity date						Apr. 01, 2029
Spire [Member] \| Maximum [Member] \| Series 2026 Senior Notes [Member] \| Master Note Purchase Agreement [Member]
Short-Term Debt [Line Items]
Debt instrument interest rate stated percentage						5.44%
Debt instrument maturity date						Apr. 01, 2038
Revolving Credit Facility [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										$ 1,500,000,000
Line of credit facility maturity date										Oct. 11, 2030
Long-term line of credit										$ 0
Revolving Credit Facility [Member] \| Maximum [Member]
Short-Term Debt [Line Items]
Line of credit facility covenant percentage of total capitalization										70.00%
Revolving Credit Facility [Member] \| Spire [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										$ 275,000,000	$ 525,000,000
Revolving Credit Facility [Member] \| Spire Missouri [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										700,000,000
Revolving Credit Facility [Member] \| Spire Alabama Inc [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										275,000,000
Revolving Credit Facility [Member] \| Spire Tennessee [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										250,000,000
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Spire [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity										$ 0		$ 725,000,000
Maturity term	364 days
Line of credit facility maturity date	Mar. 30, 2027
Line of credit facility, ticking fee for unused portion of commitments, percent per annum	0.225%
Line of credit facility, frequency of commitment fee payment	The Credit Agreement also provides for a ticking fee of 0.225% per annum on the unused portion of the commitments, accruing beginning 90 days after the effective date and continuing until the earlier of the funding date or termination of the commitments
Debt instrument, payment terms	Borrowings under the Credit Agreement bear interest, at the Company’s election, at either a base rate or an adjusted term SOFR rate plus 0.85%. The Credit Agreement also provides for a ticking fee of 0.225% per annum on the unused portion of the commitments, accruing beginning 90 days after the effective date and continuing until the earlier of the funding date or termination of the commitments. The Company has elected for all tranches to bear interest initially at a rate per annum equal to Adjusted Term SOFR, with an interest period of one month, plus 0.85%.
Maximum consolidated capitalization ratio percentage	70.00%
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Spire [Member] \| Base Rate [Member]
Short-Term Debt [Line Items]
Debt instrument basis spread on variable rate	0.85%
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Spire [Member] \| SOFR [Member]
Short-Term Debt [Line Items]
Debt instrument basis spread on variable rate	0.85%
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Bridge Term Loan [Member] \| Spire [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity												125,000,000
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Delayed Draw Term Loan (DDTL) [Member] \| Spire [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity	$ 800,000,000											$ 600,000,000
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Delayed Draw Term Loan (DDTL) [Member] \| Spire [Member] \| Tranche A [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity	600,000,000
Tennessee Natural Gas [Member] \| Senior Unsecured Facility [Member] \| Delayed Draw Term Loan (DDTL) [Member] \| Spire [Member] \| Tranche B [Member]
Short-Term Debt [Line Items]
Line of credit facility maximum borrowing capacity	$ 200,000,000